Ballasted incandescent projection lamp



July 11, 1967 R. E. SMITH 3,330,984

BALLASTED INCANDESCENT PROJECTION LAMP Filed May 27, 1965 RICHARD E. SMITH INVENTOR.

United States Patent 3,330,984 BALLASTED INCANDESCENT PROJECTIQN LAMP Richard E. Smith, Lexington, Ky., assiguor to Sylvania Electric Products Inc., a corporation of Delaware Filed May 27, 1965, Ser. No. 459,193 2 Claims. (Cl. 313115) ABSTRACT OF THE DISCLOSURE The disclosure shows a projection lamp having an incandescible filament at the focus of a reflector, and another incandescible filament in series with the first one and outside the focus of the reflector, the second filament being designed to operate at lower temperature than the first. There can be a common support wire for the adjacent ends of the filaments, said support not being connected to a lead-in wire. The second filament inhibits the tendency to arcing at lamp burnout, and reduces the effect of vibration on the filament during its life.

Description 0 the invention This application claims subject matter disclosed in applicants copending application Ser. No. 178,625, filed Mar. 9, 1962, now Patent No. 3,222,567, granted Dec. 7, 1965.

This invention relates to incandescent lamps, and particularly to lamps suitable for use in projection apparatus. In such apparatus the filament of the lamp is generally placed at or near the focus of a lens or mirror. In many such lamps, a mirror is placed inside the enclosing envelope of the lamp itself.

Such lamps are often used in motion picture projectors and in other places where there is considerable vibration. The resonant frequency of the filament coil is sometimes at or near the fundamental frequency of the projector vibration. The resultant transfer of vibration to the filament coil can therefore be very great, damaging the coil and shortening the life of the lamp. Moreover, the full lamp voltage is available across the filament, and this can result in an are at the first development of a hot spot or of a break in the coil.

To protect the filament, the end turns of the coil have generally been pulled out somewhat, that is, the pitch was decreased, to provide as much mechanical cushioning as possible for the portion of the filament between the pulled-out turns.

However, where the vibration of the projector was of considerable magnitude, the above expedient was not always satisfactory. A more effective solution of the problem was necessary for such cases.

I have now found that the damaging effects of vibration can be greatly reduced by placing in series with a main or active coil, which is placed at or near the focus of the reflector or lens, a second or ballast coil which is outside the focus of the reflector, if one is used, but which is in any event outside the field of the optical system for which the lamp is designed. I find that this provides a damping resistance which inhibits the tendency to destructive arcing across the first coil. The use of this ballast filament allows additional support for the active filament, thereby increasing the resistance of the latter to mechanical shock. Moreover, in following my invention the resonant frequency of each filament coil can be different from that of the single coil formerly used and can be adjusted independently to a value different from that of the projector itself.

Despite the loss of power in the ballast filament, which is outside the field of the optical system and which does not contribute to the useful illumination, the total quan- 3,330,984 Patented July 11, 1967 tity of light falling on the film gate from the lamp filament in the field of the lens can be kept the same as without the additional filament, that is with merely the single filament, previously used, and with no more power to both filaments than had previously been used with one. This result is unexpected, but probably arises because the entire filament, in a single filament lamp, particularly if the lamp operates at the usual line voltage, is not usefully located wtih respect to the reflector or the optical system.

In one embodiment of the invention, the ballast filament coil took 60% of the input to the lamp, and the active filament only 40%, yet the brightness at the film gate was the same as for previous lamps in which the -volt line voltage was placed across the entire filament.

In the device of my invention, the coil supporting members between the main coil and the ballast coil increase the coil strength, and the supports for the outside ends of the two-filament combination, that is, the supports to which the lamp voltage is applied, can be sufficiently spaced to decrease the tendency to destructive arcing. Moreover the ballast coil can be designed independently of the active filament in a manner such as to attain steady state temperatures in a time shorter than the time required by the main coil. This will damp the inrush current to the active coil, thereby extending the time at which a weakened spot or hot spot will cause lamp failure.

The ballast coil will inhibit the tendency to arc, by

lengthening the gap between the conductors between which the full lamp Voltage is applied. This is because an incipient arc causes an increase in current, which in turn causes an increase in voltage drop across the ballast coil, thereby sharply reducing the voltage available for sustaining the arc arcoss the active gap. The incipient arc will therefore be prevented from increasing to the full arc current necessary to destroy the terminal connections of the main coil.

The ballast coil should have a longer life than the active coil, 50 that when the latter burns out the ballast coil will still be intact to limit the current in the resultant arc. One way to achieve that result would be to make the ballast coil of wire having a diameter larger than that of the active coil, but the ballast coil would then reach its final, steady-state temperature later than the active coil would, and since the resistance of a tungsten filament rises markedly with temperature, the full resistance of the ballast coil at its highest temperature would not be reached in time to damp the initial rush current in the active coil. To insure that the ballast coil reaches its full temperature, and hence its full resistance, prior to the active coil, the ballast coil must be of wire smaller in diameter than that of the active coil. The requirements for long life and quick heating were thus opposite, and presented a serious problem. I have discovered, however, that if the ballast coil is wound to have a more open pitch than the active filament, that is, if it has fewer turns per inch, smaller wire can be used so that the ballast coil will come up to temperature quickly, while the coil will still operate at a temperature lower than that of the active coil and thus have longer life than the latter.

The turns of the active coil must be placed closer together in order to operate at high etficiency and high temperature, and to keep the greater part of the coil within the field of the optical system.

Projection lamps of the types described are operated with a filling of an inert gas in the enclosing envelope. The gas used is generally 50% argon and 50% nitrogen, the high nitrogen content being necessary to reduce the tendency toward arcing before coil burnout as well as destructive arcing on burnout. However, when the ballast "I cl? coil of my invention is present, the percentage of argon in the mixture can be increased, for example, up to 85% or more of the total gas filling, thereby increasing the efliciency and brightness considerably.

As a result of our invention the lamp will have a longer life at a given coil efliciency, especially the life under vibration, and the coil as a whole will be stronger and more rugged.

Since the enclosing envelope of the lamp will generally be tubular or of other curved shape, the ballast filament should not be placed in a position where the light or other radiation from it will be focussed or directed onto the reflector by the bulb itself. The bulb is light-transmissive but the reflection from its surface can still be as high as 10% of the total light, and that can be of appreciable absolute amount, sometimes sufl'lcient to damage the reflector by overheating it, or to result in secondary reflection of light in undesired directions. The same is true of the active filament, but the latter is less likely to be placed in a position Where reflection from the glass would be deleterious.

The ballast filament need not be of the same material as the active filament, and can be made of resistance wire such as Nichrome, but in this this case would take up considerably more room in the bulb. The Nichrome would, however, have the advantage of being even more effective in preventing surges of current at starting, because its temperature coefficient of resistance is smaller than tungsten. A material with a negative temperature coeflicient ofresistance would be very effective in that respect.

Other advantages, objects and features of the invention will be apparent from the following specification, taken in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view of one lamp embodying the invention;

FIG. 2 is a perspective view of another lamp embodying the invention;

FIG. 3 is a view of another type of fuse for the lamps;

FIG. 4 shows still another type of fuse;

FIG. 5 shows a different arrangement of the filament coils;

FIG. 6 shows still another arrangement;

FIG. 7 shows the fuse of FIG. 4 in a different position;

FIG. 8 is a front elevation and also a profile of a mount structure in which the reflector and filaments are supported from an insulating bead; and

FIG. 9 is a front elevation of a modification of the structure of FIG. 8, in which one point of the filament is supported from the reflector instead of from the bead.

In FIG. 1, the active filament 1 is at or near the focus of the reflector 2, and the ballast filament 3 is out of the focus of the reflector 2 and in front of the latter near its lower rim. The ballast filament 3 is therefore well out of the field of any optical system with which the reflector 2 is designed to be used. In the present case, the optical system can include the filament 1 and reflector 2, the latter focussing the light from said filament onto a film gate, across which a motion picture film may pass. The device can, however, be used for other purposes than the illumination of a motion picture.

The active filament 1 is supported between support wires 4, 5, to one of which it is electrically connected at each of its ends. Support wire 5 also supports, and is electrically connected to, one end of ballast filament 3, the other end being electrically connected to and supported by support wire 6, which in turn is attached to fuse wire 7, that wire then being attached to the additional support and connecting wire 8 and lead-in contact prong 9.

Support wires 4, 5 pass through a ceramic button 10 extending through and attached to reflector 2 at the apex of the latter. Support wire 5 terminates at the other side of button 16, being eld in place by a cross-wire 11 to which it is welded; support wire 4 emerges from the button, on the opposite side from the filament, and is welded to a support wire 12, which also serves as an electrical connecting wire, extending to lead-in contact prong 13. The other two lead-in contact prongs 14, 15 extend, respectively, to the short support 19, which help to support reflector 2 at its bottom rim. The center of the reflector is supported by the wire 12 which is welded, as previously stated, to the lead-in and support wire 5, extending through ceramic insulating button 10, attached to reflector 2.

In this example, as in others, the lead-in contact prongs 9, 13, 14-, 15 are sealed through a substantially fiat glass header 16, as shown in United States Patent No. 2,980,- 818, granted Apr. 18, 1961 to I. M. Harris et al. A glass bulb 17 extends from the header 16, to which it is hermetically sealed, thereby enclosing the reflector 2 and filaments 1 and 3, and their internal supports. A metal cap 18 is placed around the bottom of the bulb 17 and encloses the header 16, as in the application previously mentioned. The cap 18 has openings in its bottom through which the contact prongs 9, 13, 14, 15 extend, they being insulated from the cap 18.

It will be seen that the two filaments are in series, with the common support wire 5 connected to each filament. The active filament 1 is designed to have the desired optical properties, as to size, temperature, position, and the like, while ballast filament 3 limits the current through filament 1, and will continue to limit the current between lead-in wires 4 and 5 when filament 1 eventually burns out and an arc is established between those two lead-in wires. The are will not ordinarily spread to support wire 6, because the gap would be too long; but if it should, the fuse 7 will burn out and make the arc gap even longer.

In FIG. 1 the two filaments, or the extensions of their center lines, are roughly parallel to each other; in FIG. 2, they are perpendicular, because the active filament 1 is transverse to the axis of the bulb 17. Otherwise FIGS. 1 and 2 are the same, with the same reference numbers, except that the support wire 6 is not shown as including a fuse 7 but goes instead directly to lead-in contact prong 9. However, in practice a fuse will generally be used in the lamp of FIG. 2, just as in FIG. 1.

FIG. 3 shows an alternative arrangement for the fuse and support wire unit 6, 7, 8, in which the fuse 7 and the ends of support wires 6, 8 are sealed into a glass bead 20. This provides a more rigid support than the arrangement of FIG. 1, since the fuse wire 7 may not be of strong material. In FIG. 4, a glass head 20 is sealed between the ends of support wire 6 and lead-in contact prong 9. the fuse wire 7 thus electrically bridging the head.

In FIG. 5, both filaments 1 and 3 are supported from the ceramic button 10, the active filament 1 being nearer the button 10. The filaments can be reversed, with ballast filament 3 nearer the button, but the former arrangement will generally be preferable. The button 10 can be inserted in the reflector 2, and support and connecting wires extended from lead-in wires 4, 6 to lead-in contact prongs 9, 13.

Still another arrangement is shown in FIG. 6, where the active filament 1 is shown between wires 21, 22 with a ballast filament 3, 3 connected on each side of the active filament. Support wires 21, 22 are inserted into button 10 and firmly affixed there, but support wires 23, 24 are connected through additional support wires, to contact prongs 9, 13.

FIGURE 7 shows a modification of the invention in which the fuse wire 7 is bridged across a glass head 20 by being welded to support wires 25 and 26, the support wire 25 being welded to the contact prong 14. Support wire 26. is welded to support wire 4 and is connected to one end of the filament 1. The other end of filament 1 is connected to a support wire 5 which is secured to ceramic button 10, through which it passes. One end of the ballast filament 3, is connected to support wire 5 and extends outwardly from the reflector, with one end of ballast filament 3 being connected to the lead-in and support wire 27 which in turn is welded to lead-in contact prong 9. The

reflector 2, as usual, can be additionally supported from two other contact prongs.

In FIGURE 8 the entire mount is supported from a glass bead 30, through which the two lead-in support wires 4, pass, through support filament 1 in front of the reflector 2 and an additional support wire 31 extends upwardly from the bead 30 and is attached firmly to the apex of the reflector 2. The lead-in 5 extends completely through the bead 30 and then turns upwardly to support one end of ballast filament 3, the other end of said filament being supported by another wire 32 which extends through bead 30 and to the contact prong 9. The support wire 4 is connected to contact prong 13. The filament 3 is considerably away from the focus of the reflector 2, and out of the range in which light will be reflected or emitted to the film gate with which it is de signed to be used. In this construction the entire unit may be assembled with the parts held in fixed position from the bead 30, and the mount afterward fixed to the lead-in contact prongs 9 and 13. If two other contact prongs are present they may be used to help support the reflector 2.

FIGURE 9 shows another type of bead-supported mount in which the common filament support wire 4 is attached by welding or some other suitable means through the reflector 2, the attachment in the figure being made to a tab 40 extending outwardly from reflector 2. This tab and its corresponding tab 41 have holes 42, 43 so that the wire 4 can be aflixed to said tabs through eyelets which may pass through the holes 42 and 43.

In FIGURES 7, 8, and 9 the contact prongs 9 to 13 are shown broken; actually, of course, they pass through the header 16 as in FIGURES 1 and 2.

In one specific example of the invention, the filament 1 was of 3.22 diameter tungsten wire wound in the usual manner in a coil of 18.4 mils outside diameter, this coil then being wound around a mandrel of 30 mils diameter to form a coiled-coil filament. The mandrel of course being afterward removed in the manner customary in the art. The coil 3 is of 3.16 mils wire wound into a coil oi 18.3 mils outside diameter, this coil then being wound around a mandrel of 35 mils diameter to form a coiledcoil, the mandrel being removed as before. A mandrel can also be used in the first coiling and then removed as is customary in the coiling art. Active coil 1 was Wound to 206.5 turns per inch and ballast coil 3 to 174 turns per inch in the first coiling. In the second they were wound to about 40 to 30 turns per inch, respectively, the ballast coil being afterward pulled out to about 20 turns per inch. The number of secondary-coiling turns in the active coil 1 was about 5, and in the ballast coil 6.5. The secondarycoiling 45 in the active coil 1 is about inch long, with Q 5 turns, the straight singly-coiled legs 46 making the over all coil length between supports about 4 inch long. The ballast coil 3 is pulled out so its 6 /2 secondary turns 47 extend for about 1 inch, with the legs making the total coil length between supports about inch.

The support wires 4 and 5 were of about 25 mils diameter nickel wire, as were also the support wires 6, 8, 12, 19, and 11. The reflector can be similar to that shown in the patent to Harris et al. referred to above or can be a so-called dichroic reflector as shown in application Ser. No. 24,101, filed Apr. 22, 1960 by R. Scoledge and R. Schimer, J r.

In FIGURES 1 and 2 the projection 44 is one of three similar projections which help to align the lamp in its socket. In FIGURES 8 and 9 the reflector support wire 21 can be aflixed to the reflector by the buttons 45, 46 welded thereto.

In order to avoid local overheating of the glass in the bulb 16 and header 17, the ballast coil 3 is placed in a position Where a considerable portion of the light and other radiation from it will be transmitted through the bulb. For this reason, a ballast coil 3 with its axis parallel to the axis of the bulb, as in FIGS. 1 and 2, is very useful. It might be convenient to place the ballast coil 3 in a ceramic wafer or the like inserted between header 17 and metal cap 18, but this would cause considerable heating of the header and socket.

What I claim is:

1. An electric incandescent reflector lamp comprising an enclosing envelope, a reflector in said envelope, an active filament coil substantially at the focus of said reflector, a second filament coil outside the focus of said reflector and electrically in series with said active filament coil, a lead-in wire connected to one end of the main filament coil, a lead-in wire to one end of the second filament coil and a common support wire connecting the other end of the main filament coil to the other end of the second filament coil, said support wire being entirely within said envelope and out of contact with any wires extending outside said envelope except through said filaments.

2. An electric incandescent reflector lamp comprising an enclosing envelope, a reflector in said envelope, a main filament coil substantially at the focus of said reflector, a second filament coil outside the focus of said reflector and electrically in series with said main filament, and a common support wire connecting one end of the main fiilament coil to one end of the second filament coil, the second coil having its longitudinal axis substantially parallel to the longitudinal axis of the envelope.

References Cited UNITED STATES PATENTS 3,023,667 3/1962 Lessman 313 X 3,222,567 12/1965 Smith 315-71 JAMES W. LAWRENCE, Primary Examiner.

R. JUDD, Assistant Examiner. 

1. AN ELECTRIC INCANDESCENT REFLECTOR LAMP COMPRISING AN ENCLOSING ENVELOPE, A REFLECTOR IN SAID ENVELOPE, AN ACTIVE FILAMENT COIL SUBSTANTIALLY AT THE FOCUS OF SAID REFLECTOR, A SECOND FILAMENT COIL OUTSIDE THE FOCUS OF SAID REFLECTOR AND ELECTRICALLY IN SERIES WITH SAID ACTIVE FILAMENT COIL, A LEAD-IN WIRE CONNECTED TO ONE END OF THE MAIN FILAMENT COIL, A LEAD-IN WIRE TO ONE END OF THE SECOND FILAMENT COIL AND A COMMON SUPPORT WIRE CONNECTING THE OTHER END OF THE MAIN FILAMENT COIL TO THE OTHER END OF THE SECOND FILAMENT COIL, SAID SUPPORT WIRE BEING ENTIRELY WITHIN SAID ENVELOPE AND OUT OF CONTACT WITH ANY WIRES EXTENDING OUTSIDE SAID ENVELOPE EXCEPT THROUGH SAID FILAMENTS. 